Global positioning system (GPS) and doppler augmentation (GDAUG) and space location inertial navigation geopositioning system (SPACELINGS)

ABSTRACT

A global positioning system (GPS) and Doppler augmentation (GDAUG) end receiver (GDER) can include a GDAUG module. The GDAUG module can generate a GDER position using a time of flight (TOF) of a transponded GPS signal and a Doppler shift in a GDAUG satellite (GSAT) signal. The transponded GPS signal sent from a GSAT to the GDER can include a frequency shifted copy of a GPS signal from a GPS satellite to the GSAT. The GSAT signal can include a signal generated by the GSAT to the GDER.

BACKGROUND

Satellite navigation systems, such as a global positioning system (GPS),enable a receiver to determine a location from ranging signals receivedfrom a plurality of satellites. The GPS can include three majorsegments: a space segment (SS), a control segment (CS), and a usersegment (US). The United States Air Force develops, maintains, andoperates the space and control segments. GPS satellites broadcastsignals from space, and each GPS receiver uses these signals tocalculate a three-dimensional location (latitude, longitude, andaltitude) of the GPS receiver and a current time at each GPS satellite.The space segment can include 24 to 32 satellites in a medium Earthorbit (MEO). The control segment can include a master control station,an alternate master control station, and a host of dedicated and sharedground antennas and monitor stations. The user segment can includemilitary, civil, commercial, and scientific users.

SUMMARY OF EXEMPLARY EMBODIMENTS

The ranging signals can be broadcasted on frequencies, such as the L1signal (1.57542 gigahertz (GHz)) and/or L2 signal (1.2276 GHz). Positioncan be determined from matching codes in the transmitted signal and thereceiver to determine the difference in time between transmission andreception. A code division multiple access (CDMA) code is transmitted bythe GPS satellites to the receiver and correlated with replica codes todetermine ranges to different satellites, which can be used to determinethe position of a GPS receiver on or near the Earth. Generally, a GPSreceiver receives signals from multiple GPS satellites (e.g., four) tofind its position.

In some exemplary embodiments, a global positioning system (GPS) andDoppler augmentation (GDAUG) end receiver (GDER) can be provided, whichcan comprise a GDAUG module, wherein the GDAUG module can generate aGDER position using a time of flight (TOF, the difference in timebetween transmission and reception) of a transponded GPS signal and aDoppler shift in a GDAUG satellite (GSAT) signal, and wherein thetransponded GPS signal sent from a GSAT to the GDER can comprise afrequency shifted copy of a GPS signal from a GPS satellite to the GSAT,and the GSAT signal can comprise a signal generated by the GSAT to theGDER.

The GDAUG module can further comprise a Doppler shift module thatmeasures a Doppler shift in the GSAT signal, a GSAT ephemeris estimatorthat can determine a GSAT position by measuring a trend in a pluralityof GSAT Doppler shift measurements from a plurality of GSAT signals, anda range estimator that can calculate a GSAT range from the GSAT positionand a super-range measurement of the transponded GPS signal, wherein thesuper-range measurement can represent a distance from the GPS to theGDER via the GSAT. A receiver location estimator that can estimate aGDER position using the GSAT position and the GSAT range may also beincluded in the GDAUG module.

The Doppler shift module can measure a Doppler shift in the transpondedGPS signal, and the GSAT ephemeris estimator can determine the GSATposition by extracting the Doppler shift due to the GSAT range from theDoppler shift of the transponded GPS signal to generate a Doppler shiftof the GPS signal and by estimating the GSAT position using the Dopplershift of the GPS signal.

An exemplary method for global positioning using a global positioningsystem (GPS) and Doppler augmentation (GDAUG) end receiver (GDER) canalso provided, which method can comprise generating a GDER positionusing a time of flight (TOF) of a transponded GPS signal and a Dopplershift in a GDAUG satellite (GSAT) signal, wherein the transponded GPSsignal sent from a GSAT to the GDER can comprise a frequency shiftedcopy of a GPS signal from a GPS satellite to the GSAT, and the GSATsignal can comprise a signal generated by the GSAT to the GDER.

Generating the GDER position can further comprise generating asuper-range measurement from the transponded GPS signal, wherein thesuper-range measurement can represent a distance from the GPS to theGDER via the GSAT, measuring a Doppler shift in the GSAT signal,determining a GSAT position by measuring a trend in a plurality of GSATDoppler shift measurements from a plurality of GSAT signals, calculatinga GSAT range from the GSAT position and the super-range measurement ofthe transponded GPS signal, and estimating a GDER position using theGSAT position and the GSAT range.

A computer program product can also be provided, which computer programproduct can comprise a non-transitory computer readable storage mediumhaving a computer readable program code embodied therein, the computerreadable program code being adapted to be executed to implement themethod discussed above.

A global positioning system (GPS) and Doppler augmentation (GDAUG)satellite (GSAT) can also be provided, which can comprise a GPS signalreceiver for receiving a GPS signal, a frequency shifter for generatinga transponded GPS signal from the GPS signal using a GSAT frequency bandsubstantially different from a GPS signal frequency band, a signalgenerator for generating a GSAT signal, and a signal transmitter fortransmitting the transponded GPS signal and the GSAT signal to a GDAUGend receiver (GDER).

BRIEF DESCRIPTION OF THE DRAWINGS

Features and advantages of the disclosure will be apparent from thedetailed description which follows, taken in conjunction with theaccompanying drawings, which together illustrate, by way of example,features of the disclosure; and, wherein:

FIG. 1 illustrates a diagram of a plurality of global positioning system(GPS) satellites, a GPS and Doppler augmentation (GDAUG) satellite(GSAT), and a GDAUG end receiver (GDER) in accordance with an example;

FIG. 2A illustrates a block diagram of a global positioning system (GPS)and Doppler augmentation (GDAUG) satellite (GSAT) in accordance with anexample;

FIG. 2B illustrates a block diagram of a global positioning system (GPS)and Doppler augmentation (GDAUG) satellite (GSAT) with an amplifier inaccordance with an example;

FIG. 3 illustrates a diagram of a plurality of global positioning system(GPS) satellites, a plurality of GPS and Doppler augmentation (GDAUG)satellites (GSAT), and a GDAUG end receiver (GDER) in accordance with anexample;

FIG. 4A illustrates a block diagram of a global positioning system (GPS)and Doppler augmentation (GDAUG) end receiver (GDER) in accordance withan example;

FIG. 4B illustrates a block diagram of a global positioning system (GPS)and Doppler augmentation (GDAUG) end receiver (GDER) with a GPS receiverin accordance with an example;

FIG. 5 depicts a flow chart of a method for global positioning using aglobal positioning system (GPS) and Doppler augmentation (GDAUG) endreceiver (GDER) in accordance with an example;

FIG. 6 depicts a flow chart of a method for global positioning using aglobal positioning system (GPS) and Doppler augmentation (GDAUG)satellite (GSAT) in accordance with an example;

FIG. 7 illustrates a diagram of a high altitude satellite (HAS), aplurality of space location inertial navigation geopositioning system(SPACELINGS) satellites (SLS), and a plurality of SPACELINGS endreceivers (SER) in accordance with an example;

FIG. 8 illustrates a block diagram of a high altitude satellite (HAS), aspace location inertial navigation geopositioning system (SPACELINGS)satellite (SLS), and a SPACELINGS end receiver (SER) in accordance withan example;

FIG. 9 depicts a flow chart of a method for global positioning using aspace location inertial navigation geopositioning system (SPACELINGS)end receiver (SER) with at least two downlink PRN signals from a highaltitude satellite (HAS) in accordance with an example;

FIG. 10 depicts a flow chart of a method for global positioning using aspace location inertial navigation geopositioning system (SPACELINGS)end receiver (SER) with a downlink PRN signal from a high altitudesatellite (HAS) in accordance with an example;

FIG. 11 illustrates a diagram of a global positioning system (GPS)satellite, a plurality of space location inertial navigationgeopositioning system (SPACELINGS) satellites (SLS), and a plurality ofSPACELINGS end receivers (SER) in accordance with an example;

FIG. 12 illustrates a block diagram of a global positioning system (GPS)satellite, a space location inertial navigation geopositioning system(SPACELINGS) satellite (SLS), and a SPACELINGS end receiver (SER) inaccordance with an example;

FIG. 13 depicts a flow chart of a method for global positioning using aspace location inertial navigation geopositioning system (SPACELINGS)end receiver (SER) with at least two global positioning system (GPS)signals from a GPS satellite in accordance with an example;

FIG. 14 illustrates a diagram of a high altitude satellite (HAS), aplurality of space location inertial navigation geopositioning system(SPACELINGS) satellites (SLS), a plurality of SPACELINGS end receivers(SER), and a ground station (GS) in accordance with an example;

FIG. 15 illustrates a block diagram of a ground station (GS), a highaltitude satellite (HAS), a space location inertial navigationgeopositioning system (SPACELINGS) satellite (SLS), and a SPACELINGS endreceiver (SER) in accordance with an example; and

FIG. 16 illustrates a diagram of sample position error for the north,east, and down positions for a non-accelerating end receiver inaccordance with an example.

Reference will now be made to the exemplary embodiments illustrated, andspecific language will be used herein to describe the same. It willnevertheless be understood that no limitation of the scope of theinvention is thereby intended.

DETAILED DESCRIPTION

Before the present invention is disclosed and described, it is to beunderstood that this invention is not limited to the particularstructures, process steps, or materials disclosed herein, but isextended to equivalents thereof as would be recognized by thoseordinarily skilled in the relevant arts. It should also be understoodthat terminology employed herein is used for the purpose of describingparticular examples only and is not intended to be limiting. The samereference numerals in different drawings represent the same element.Numbers provided in flow charts and processes are provided for clarityin illustrating steps and operations and do not necessarily indicate aparticular order or sequence.

Example Embodiments

An initial overview of technology embodiments is provided below and thenspecific technology embodiments are described in further detail later.This initial summary is intended to aid readers in understanding thetechnology more quickly but is not intended to identify key features oressential features of the technology nor is it intended to limit thescope of the claimed subject matter.

The global positioning system (GPS) is a space-based global navigationsatellite system (GNSS) that can provide location and time informationin various types of weather, anywhere on or near the Earth, where a GPSreceiver has an unobstructed line of sight to four or more GPSsatellites. When a GPS satellite is blocked from the GPS receiver so toofew GPS satellites are in view of the GPS receiver, the GPS receiver canprovide no positioning information or it can generate inaccurate orincorrect positioning information. Alternatively, the GPS signal onknown GPS frequencies may be jammed by an external jamming source orother electronic equipment preventing the GPS receiver from receiving avalid GPS signal. Alternatively, an external spoofing source maygenerate a false GPS signal on known GPS frequencies in an attempt tospoof the GPS receiver to generate inaccurate or incorrect positioninginformation.

FIG. 1 illustrates a segment of a GPS and Doppler augmentation (GDAUG)satellite (GSAT) system, which can be used to provide GPS-type positionaccuracy to an end receiver using frequency shifted copies of GPSsignals 142A-C relayed through a GSAT 130, referred to as transpondedGPS signals or symbolically represented by a S1 signal. A transpondedsignal can be frequency shifted copy of an original signal transpondedfrom a different location. A repeated signal can be a copy of theoriginal signal repeated from the different location. In someembodiments, the transponded signal can include the repeated signal, butgenerally the transponded signal is a frequency shifted copy of theoriginal signal. The GPS signals can include the L1 and/or the L2signals. The GSAT can generate a S1 signal for either the L1 or L2 GPSsignal received. The end receiver capable of receiving GSAT signals canbe referred to as a GDAUG end receiver (GDER) 120. The GDER can be on ornear the Earth 110. The GDER can measure the time difference between thegeneration of the signal by a GPS and the reception of S1 to generate asuper-range measurement representing the distance from a GPS satellite140A-C to the GDER via the GSAT (or a GPS-to-GSAT-to-GDER range). TheL1, L2, and/or S1 can include a pseudo-random noise code (PRN or PNcode), which includes a time the L1 or L2 signal was generated by theGPS. The super-range measurement can include a time of flight (TOF) ofthe L1 or L2 signal plus the TOF of the S1 signal. The GDER can alsomeasure the Doppler shift of S1, which can have a Doppler shiftcontribution from the transmission from GPS to GSAT and GSAT to GDER.

A super-range can include two legs of a “bent pipe” that can include aGPS-to-GSAT range, represented by the TOF of L1 or L2 142A-C, and aGSAT-to-GDER range, represented by the TOF of S1 132. The S1 signal,which can be a copy or a frequency shifted copy of the L1 or L2 signal,can encode the position of the GPS satellites. The GDER can receive theS1 signal and determine the time elapsed between the signal origin andthe receiver's time. The GDER can also read the encoded GPS positioninformation.

The GSAT can also generate a GSAT signal, such as a tone, that can beused to determine the Doppler shift due to the GSAT-to-GDER path. Thetone can be a sinusoidal wave at specified frequency. The GSAT signalcan be symbolically represented by a S2 signal. The S1 signal and the S2signal can be transmitted 132 from the GSAT to the GDER. Measuring atrend in Doppler shift of the S2 signal can allow the GDER to determinethe ephemeris of the GSAT. Having information on the ephemeris of theGSAT, the GDER can determine the distances of the two legs of thesuper-range, and accordingly the range from GSAT to GDER. The range mayhave some error if a timing offset between the GPS time on a GPSsatellite clock and a clock used by the GDER occurs. The ephemeris caninclude a table various information, such as the positions or orbits ofa heavenly body (e.g., a satellite) on a number of dates and times in aregular sequence. Although three GPS satellites are shown in FIG. 1, theGSAT location and the GDER location may be determined with one GPSsatellite in some scenarios.

The carrier frequencies of the S1 and S2 signals may be selected tominimize and avoid jammed portions of the spectrum. The GDER cancontinue to measure range from GSAT and can measure and trend over timethe Doppler shift in S1 due to the transmission from GSAT to GDER. Therange and Doppler trend data from one or more GSATs can be used by theGDER to estimate the GDER's three dimensional (3-D) position.

The GDER utilizing the GDAUG system can enable users to navigate whenGPS signals are jammed or spoofed, and can provide positioningassistance to a user that is not in view of a sufficient number of GPSsatellites. The GDAUG system can also add precision to the existing GPS.

In another example, the GDER can use range measurements (including asuper-range measurement generated from a TOF of a transponded GPSsignal) and Doppler measurements to estimate the GDER's position. TheDoppler measurements can be trended over time. To obtain rangemeasurements, the GDER can decode the contents of a GPS signaltransponded by a GSAT. Decoding the transponded GPS signal can reveal aposition of the GPS that originated the GPS signal and can provide apsuedo-random noise (PRN) signal from which a super-range (or distancefrom the GPS satellite to the GSAT, then to the GDER) can be estimated.To obtain a range (including the GSAT-to-GDER range and the GPS-to-GSATrange) from the super-range, the GDER can estimate an ephemeris (ororbit) of the GSAT and subtract (or otherwise remove) the GSAT ephemeriscomponent of range from the super-range. The S2 signal can enable thereceiver to estimate the ephemeris of the GSAT. The S2 signal can alsohelp separate the Doppler shift measured on the S1 signal into a partdue to transmission from the GPS satellite to GSAT and a part due totransmission from the GSAT to GDER. The Doppler shift of the part of theS1 signal due to transmission from the GPS satellite to GSAT can also beused to help estimate the ephemeris of the GSAT. The combination ofDoppler shift of the S1 due to transmission from GSAT to GDER and therange measurements from GSAT to GDER can enable the GDER to estimate theGDER's position.

Some errors in the system can occur due to clock offsets/bias betweenthe GDER clock and the GPS satellite clocks. The biases can be resolvedover time due to a moving position of the GSAT, in one aspect, and/or byan altitude sensor or barometric sensor in another aspect.

Although not to be limiting in any way, the GSATs in the GDAUG systemcan be a CUBESAT or other similar type of small or inexpensive typesatellite. The CUBESAT can be a type of miniaturized satellite. In oneembodiment, the CUBESAT can comprise a volume of approximately a liter(10 centimeter (cm) cube) with a weight less than 5 kilograms, andpreferably less than 2 kilograms (kg). The CUBESAT can use commercialoff-the-shelf electronics components. The GSAT can include functions,such a power source or a power generation mechanism, a mechanism tocontrol heating and cooling of the satellite, and/or a mechanism topoint a transmitter or antenna to the Earth. The power generationmechanism can include solar cells or panels. The power source caninclude a battery or capacitive device. The mechanism to control theheating and cooling of the satellite may control the heating and coolingof the satellite passively, so the mechanism does not require a powersource to function properly. The mechanism to point the transmitter orantenna to the Earth may steer or rotate the position of the satellitepassively.

Each GSAT can act as a bend in a “bent pipe” between a GPS satellite andthe GDER and can provide a transponder relay of the GPS signals. Thetransponder can detect the analog radio frequency (RF) signals receivedby the GPS satellite, shift the frequency of the signal to a morefavorable and/or unjammed frequency, and transmit the frequency shiftedGPS signal (S1 signal). In another example, the GSAT can providefrequency hopping of the S1 signal.

As illustrated in FIG. 2A, the GSAT 130 can include at least onereceiving antenna 210, a GPS signal receiver 220 (GPS receiver) forreceiving a GPS signal (or plurality of GPS signals), a frequencyshifter 222 for generating the S1 signal from the GPS signal (L1 or L2),a signal generator 230 for generating the S2 signal, at least onetransmitting antenna 212, and/or a signal transmitter 240 fortransmitting the S1 signal and/or the S2 signal to the GDER. The S1signal and/or the S2 signal can be transmitted to the GDER in a simplextransmission. The simplex transmission is one-way communication orcommunication that occurs in one direction only (in contrast to duplextransmission or two-way communication). The transmitting antenna can bea wide angle antenna to cover the Earth from a low orbit. The antennagain can be limited with a wide angle antenna. The receiving antenna andthe transmitting antenna can be a single antenna or a duplex antenna aslong as the antenna can both receive a GPS signal and transmit the S1and S2 signals. The S1 signal and the S2 signals can use a GSATfrequency band substantially different from the GPS signal. Asubstantially different GSAT frequency band can be a band that is not aGPS frequency band received by a typical GPS receiver. GPS satellitestransmit L1 GPS signals on a common set of frequency carriers and in thesame frequency bands. Similarly, L2 signals can be transmitted on adifferent common carrier frequency. The S1 signals and the S2 signal canoperate in a frequency band (the GSAT frequency band) between a veryhigh frequency (VHF) band to a K-under (K_(u)) band. The VHF band is theradio frequency range from 30 megahertz (MHz) to 300 MHz, and the K_(u)band is the radio frequency range from 10.95 gigahertz (GHZ) to 14.5 GHzor the band directly below the K-band. The K-band is the radio frequencyrange from 18 GHz to 27 GHz. The GSAT frequency band can include theVHF, an ultra high frequency (UHF), and portions of a super highfrequency (SHF) band, such as the K_(u) band. In another exampleillustrated in FIG. 2B, the GSAT can also include an amplifier 250 foramplifying the received GPS signal, the S1 signal, and/or the S2 signal.

As illustrated in FIG. 3, the GDAUG system can include a constellationof low Earth orbit (LEO) satellites (or a plurality of GSATs 130A-H).LEO can generally be defined as an orbit within the locus extending fromthe Earth's surface 110 up to an altitude of approximately 2,000kilometers (km). The GSAT can be a LEO satellite. A GPS can operate witha constellation of 24 GPS satellites 140A-J. The GPS satellites can bemedium Earth orbit (MEO) satellites. MEO, also known as an intermediatecircular orbit (ICO), can be a region of space around the Earth abovethe LEO (altitude of approximately 2,000 km or 1,243 miles (mi)) andbelow geostationary orbit (altitude of 35,786 km or 22,236 ml). Thegeostationary orbit, also known as the geostationary Earth orbit (GEO),can have a period equal to the Earth's rotational period and an orbitaleccentricity of approximately zero. An object in the GEO can appearmotionless, at a fixed position in the sky, relative to groundobservers. The GSAT may be in an orbit between a GPS satellite and asurface of the Earth.

The number of GSATs in the GSAT constellation may be greater than thenumber of GPS satellites in the GPS constellation to provide globalcoverage or near global coverage. For example, 66 GSATs in the GSATconstellation can provide global coverage from 800 km. Fewer GSATs canbe used for non-polar coverage or if gaps can be tolerated. Each GSATcan operate independently of other GSATs.

Each GPS satellite can transmit a GPS signal to a GSAT, though as few asone may be used for GDAUG operation. For example, FIG. 3 illustratesfour GPS satellites 140A-D transmitting their GPS signal 142A-D to aGSAT 130A. In another example, a GPS satellite 140E can transmit a GPSsignal 144B-144F to five GSATs 130A-E. In another example, the GDER 120can receive the S1 and S2 signals 132A-C and 132H from four GSATs 130A-Cand 130H.

The GSAT can receive GPS signals from multiple GPS satellites, and theGSAT can transmit the S1 and S2 signals to multiple GDERs (not shown).The GDER can process the S1 and S2 signals from multiple GSATs. Usingthe GSAT in LEO instead of a GPS in MEO can reduce the power consumed totransmit the S1 and/or S2 signals by placing the GSAT closer to theGDER. The GSAT can have a much lower cost, simpler design, and fewercomponents than a GPS. For example, a GSAT may be configured so as tonot include an atomic clock.

Given the close range of the GSAT in LEO to the GDER, the signalstrength for the S1 or the S2 signals can be less than 10 watts (W), inan example. In another example, transmission of the S1 signal and the S2signal can be alternated to save power. In another example, thetransmission of the S1 signal and the S2 signal can transmit at regularintervals less than the GPS transmission interval to save power. In anexample, the GSAT can be a satellite with a stable orbit within the LEOor MEO. In another example, the GSAT can have an unknown ephemeris,velocity, and/or position.

A GEO satellite can have a velocity of approximately 3 km/second (sec)to match the velocity of the Earth with an apparent velocity ofapproximately 0 km/sec. The apparent velocity can be an object'svelocity, such as a satellite, relative to another object, such as a GPSreceiver or a GDER at a fixed point on the Earth. A GPS satellite canhave an apparent velocity of less than 1 km/sec relative to the fixedpoint on the Earth. The GSAT in the LEO (or other LEO satellite) canhave an orbit with an apparent velocity of approximately 5 to 7.5 km/secrelative to the fixed point on the Earth. If a GSAT has an apparentvelocity of approximately 7 km/sec relative to the fixed point on theEarth, the GSAT can have an apparent velocity of approximately 6 km/sec(7 km/sec for the GSAT−1 km/sec for the GPS satellite) relative to a GPSsatellite when the GSAT is moving towards the GPS satellite, and theGSAT can have an apparent velocity of approximately 8 km/sec (7 km/secfor the GSAT+1 km/sec for the GPS satellite) relative to a GPS satellitewhen the GSAT is moving away from the GPS satellite. Measuring the speedof the GSAT using the Doppler shift of a signal transmitted by the GSATcan be used to generate global positioning in a system to augment theGPS.

A Doppler shift can be a change in a frequency (or a change in awavelength) of a wave for an observer, such as a receiver, movingrelative to the source of the wave, such as a transmitter on asatellite. The motion of the observer, the source, or both can generatea change of the frequency. The relative changes in frequency due to theDoppler effect can be explained as follows. When the source of the wavesis moving toward the observer, each successive wave crest is emittedfrom a position closer to the observer than the previous wave.Therefore, each wave takes slightly less time to reach the observer thanthe previous wave. Thus, the time between the arrival of successive wavecrests at the observer is reduced, causing an increase in the frequency.While the waves are traveling, the distance between successive wavefronts is reduced, so the waves “bunch together”. Conversely, if thesource of waves is moving away from the observer, each wave is emittedfrom a position farther from the observer than the previous wave, so thearrival time between successive waves is increased, reducing thefrequency. The distance between successive wave fronts is increased, sothe waves “spread out”.

The Doppler shift can be proportional to the carrier frequency. Higherfrequencies can provide more accuracy in Doppler measurements than lowerfrequencies but generating higher frequencies can consume more power inthe GSAT than lower frequencies. Objects moving at greater velocitiesrelative to each other can provide more accuracy in Doppler measurementsthan objects moving at slower velocities relative to each other. Objectsat closer distances to each other can provide more accuracy in Dopplermeasurements than objects at farther distances to each other. The GSAToperating in LEO can impose a greater amount of Doppler shift on thetransponded signal than a direct signal between the GPS satellite andthe GDER. The Doppler shift of the GSAT to a known point can uniquelydetermine the orbital parameters of the GSAT. The Doppler shift can bethe shift between GPS and the GSAT and/or GSAT and the GDER

Each GPS signal received by the GSAT can experience a Doppler shift infrequency due to the relative motion between each GPS satellite and theGSAT. Thus, the GSAT can receive a different Doppler shift for each GPSsignal. The GSAT can frequency shift each GPS signal including therespective Doppler shift and generate a S1 signal for each GPS signalreceived, and transmit each S1 to the GDER. Each S1 signal received bythe GDER can also experience a Doppler shift in frequency due to therelative motion between the GSAT and the GDER. So, each transponded GPSsignal (S1) can be “double Doppler shifted” when received by the GDER.Each S1 signal can have the sum of the Doppler shift from the GPSsatellite to the GSAT (in the L1 and/or L2 signals) and the Dopplershift from the GSAT to the GDER. Due to the velocity of the GSATrelative to the GDER and the GPS satellite, the S1 signals generatedfrom the GPS satellites in view can have much greater possible Dopplerfrequency shift than GPS signals sent directly from the GPS satellitesto the GDER. The S1 signals can have the same code division multipleaccess (CDMA) codes as the original GPS signals (L1 and/or L2 signals).The GDER can despread, demodulate, and/or decode the S1 signals toobtain the ephemeris of each GPS satellite and to estimate the time ofsignal flight from GPS to the GDER via the GSAT. The time of flight canprovide a two-leg “super-range” for each S1 signal. Each super-range canbe the sum of the distances from the GPS satellite associated with theS1 signal to the GSAT and from the GSAT to the GDER.

The GDER can also receive the S2 signal generated by the GSAT. TheDoppler shift of S2 can be computed to determine a GSAT Doppler shiftmeasurement from the GSAT to the GDER. The measurement can be used todetermine a fraction of the Doppler shift of S1 due to the path from theGPS satellite to the GSAT and/or a fraction of the Doppler shift of S1due to the path from the GSAT to the GDER. The Doppler shift of each GPSsignal (L1 and/or L2) as received by GSAT can be represented by GLD_(n),for N GPS signals where N and n are positive integers and n≦N. The S1signal and the S2 signal can be transmitted on different frequencies.Each S1 signal can be transmitted on a different frequency from other S1signals. In another example, the frequency of the S1 signal and the S2signal can vary in a coordinated scheme between the GSAT and the GDER.

Each GLD_(n) can vary with time in a pattern corresponding to relativeorbits of each GPS and GSAT. The GDER can estimate the position of theGSAT using each GLD_(n) and a previously decoded ephemeris of each GPS.The estimate of ephemeris can be aided by trending the Doppler shift ofS2. Thus, a 3-D GSAT position (or GSAT orbit) and a GPS-to-GSAT rangefor each super-range measurement or value can be determined.

The remaining distance in each super-range after the associatedGPS-to-GSAT range is removed can be a GSAT range (or GSAT-to-GDERrange). A residual error in the range estimate can be due to adifference in time between the GDER clock and the GPS clock. The GSATprocessing delay can be known and can include the time between receivinga GPS signal at the GSAT and transmitting the signal from the GSAT.GDERs using more accurate oscillators can have less clock error. TheGDER clock error can be substantial (e.g., 1 microsecond [psec] cancorresponds to a 300 meter error) and can adversely affect the estimatedvolume in which the GDER is located. The estimated volume can be a long,thin cylinder whose long dimension is centered on the line between theGSAT and GDER. As the GSAT moves rapidly across the sky, a series of“error cylinders” can be generated with a long axis of each errorcylinder pointing towards the GSAT. The GDER can compute theintersections of the long cylinders to determine a final 3-D position ofGDER. Once a 3-D position of the GDER is known, the GDER can correctclock errors and update its position very precisely in 3-D coordinates.Alternatively, signals from two or more GSATs may be received inparallel or sequentially to refine the position estimate andreduce/remove the effects of clock bias.

A trend in the Doppler shift of S2 signals combined with rangemeasurements can be used to precisely determine the location of the GDER(within a small circular error) at a known altitude or with a stablealtitude. When a prior knowledge of the GDER's altitude is not known, analtimeter can be used to provide an altitude of the GDER. The altimetercan be used to initialize the altitude of the GDER. The altimeter can bea pressure altimeter or a barometric altimeter, but other types ofaltimeters can also be used, such as a sonic altimeter or a RADAR (radiodetection and ranging) altimeter. When altitude is not known, the GDERmay occupy a cylindrical region of uncertainty.

FIG. 4A illustrates an example of the GDER 120. The GDER can include aGDAUG receiver antenna 310, a GDAUG signal receiver 320, a signaldespreader 330, and a GDAUG module 340. The GDAUG receiver antennaand/or the GDAUG signal receiver can receive the S1 signals and the S2signal. The GDAUG receiver antenna may be a broad angle antenna capableof receiving continuous signals from LEO satellites. The signaldespreader can demodulate, despread, and/or decode the S1 signals. Thesignal despreader can extract the time at a GPS satellite, a GPSsatellite location, a GPS satellite identifier, and/or a GPS satelliteephemeris from the S1 signal. The signal despreader can be used todetermine the TOF of the L1 or L2 signal combined with the S1 signal (orsuper-range measurement). The S1 signal can be used to generate asuper-range measurement from the GPS satellite to the GDER via the GSAT.Each super-range measurement can represent a time of flight (TOF)distance from the associated GPS satellite to the GSAT to the GDER in abent pipe configuration. The time of the L1 or L2 signal's origin, alsoencoded in the S1 signal, can be used to generate the super-rangemeasurement. A different detector can be used to detect the S2 signal.In another example, the GDAUG module may also generate the super-rangemeasurement.

The GDAUG module 340 can generate a GDER position using a TOFsuper-range measurement, a Doppler shift in a plurality of transpondedGPS signals (S1 signals), and/or a Doppler shift in a GSAT signal (S2signals). The GDAUG module can include a Doppler shift module 342, aGSAT ephemeris estimator 344, a range estimator 346, and a receiverlocation estimator 348. The Doppler shift module can measure a Dopplershift in the S1 signals and a Doppler shift in the S2 signals. TheDoppler shift in the S1 signal can represent the double Doppler shift ofthe combined Doppler shift in the L1 or L2 signal plus the Doppler shiftin transponded L1 or L2 signal from the GSAT to the GDER. The Dopplershift in the S2 signal (or GSAT Doppler shift measurement) can be usedto derive the portion of Doppler shift of the S1 signal due to a GSAT toGDER distance. The GSAT Doppler shift measurement can provide theDoppler frequency shift due to the path from GSAT to GDER.

The GSAT ephemeris estimator can determine a GSAT position by removing,subtracting, or otherwise compensating for the GSAT Doppler shiftmeasurement in each of the super-range measurements to generateGPS-to-GSAT ranges for each super-range. The GSAT position can then begenerated from GPS satellite positions extracted from the S1 signals andthe GPS-to-GSAT ranges. The GSAT ephemeris estimator can continuallyiterate the GSAT position based on updated S1 signals, updated S2signals, updated super-ranges, updated GSAT-to-GDER ranges, and/orupdated GPS-to-GSAT ranges. The GSAT ephemeris estimator can seed orinitialize the iteration with an expected orbit for the GSAT.

The range estimator can calculate a GSAT range from the GSAT to the GDERby removing the GPS-to-GSAT range from an associated super-rangemeasurement. The receiver location estimator can estimate a GDERposition using the GSAT position and the GSAT range plus the portion ofDoppler shift of S1 from GSAT to GDER and/or the Doppler shift in S2.The range estimator can continually iterate the GDER position based onthe updated GSAT position and/or the updated GSAT range.

The GDAUG module can report and iterate the position and velocity of theGDER and GSAT along with the GSAT ephemeris. The GSAT ephemerisestimator can trend the GSAT location over time to generate aninstantaneous or average GSAT velocity and/or a GSAT ephemeris. TheDoppler shift module can trend the Doppler shift of the S1 signals andthe S2 signal to generate a 3-D GSAT location, a GSAT velocity, and/or aGSAT ephemeris. The trending of the S1 signals by the Doppler shiftmodule can be used to verify the GDER position and/or the GDER velocity.

A GDER location can be determined with greater accuracy when the GDER isstationary versus a mobile GDER. Movement in the GDER can introduceadditional errors and inaccuracies which can be corrected with trendingof the GSAT location, the trending of the Doppler shift of the S1signals, and/or the trending of the Doppler shift of the S2 signal. Aninertial measurement unit (IMU), such as a pedometer, can be included inthe GDER to account for the movement of a GDER. The IMU and/or thealtimeter can be included in the receiver location estimator of theGDER. The GDAUG module can reset the clock bias using S1 signals and/orthe 3-D GSAT location.

FIG. 4B illustrates another example of the GDER 120 to include a GPSreceiver 350. The GPS receiver can include a GPS signal receiver 352 anda GPS signal processor 352 for obtaining a global positioning of theGDER using standard GPS processing. The GPS receiver can receive GPSsignals directly from GPS satellites and determine a global position ofthe GDER using the GPS signals transmitted by the GPS satellites. TheGPS receiver can use the GDAUG receiver antenna 310 or a separate GPSreceiver antenna (not shown).

The GDER location provided by the GDAUG module (or GDAUG location) canbe compared with the GDER location provided by the GPS receiver (or GPSlocation) in a GPS and GDAUG location comparison module 360. The GPS andGDAUG location comparison module can determine a difference between theGDAUG location and the GPS location, and determine if the locations arewithin a specified tolerance. When the locations are outside a specifiedtolerance, the GDER can determine that spoofing or jamming is occurringand display or use the GDAUG location. If the GPS receiver is unable togenerate a GPS location or an accurate GPS location due to jamming ornot enough GPS satellites in view of the GDER, the GDER can use theGDAUG location. If the GDAUG module is unable to generate a GDAUGlocation or an accurate GDAUG location due to a GSAT not in view of theGDER or a GPS not in view of the GSAT, the GDER can use the GPSlocation. In another example the GDAUG module, the GPS and GDAUGlocation comparison module, and the GPS receiver can be coupled to anoutput device 370. The output device can be a display, screen, printer,an input/output (I/O) port, or transmitter that can transmit thelocation to another device. In another example, the GDER (not shown) canalso combine the processing of GPS signals, S1 signals, and S2 signalsto generate a composite GPS-GDAUG location.

When the GDER already determined the GDER position or location initially(from the GDAUG module, the GPS receiver, or other global positioningmechanism), a condition known as a hot start or steady statepositioning, signals from one or two GSATS may be used to maintain aGDER's 3-D location. The GDER location may become more accurate with alonger GDER time of operation. For example, the GDER can produceaccuracy within a 100 meter (m) range within 70 seconds of operation, 50m within 85 seconds of operation, and 25 m within 100 seconds ofoperation. The accuracy can continue to improve with time. The time toinitialize the GDER location can depend on the number of GSATs in viewand whether the GDER is moving or not. A stationary GDER may beinitialized more rapidly than a moving GDER.

The GDAUG system can provide reuse of GPS signals, GPS spoof detection,and a backup global positioning system if the GPS is jammed or spoofed.The GDAUG system can provide simplex communication, which can be faster,more accurate, and use less satellite processing than TRANSIT (apredecessor system to GPS, also known as Navy Navigation SatelliteSystem [NAVSAT]), the duplex communication systems of GLOBALSTAR (a LEOsatellite constellation for satellite phone and low-speed datacommunications) or GATEWAY and other duplex communication systems. TheGDAUG system can be used when fewer than three GPS satellites have adirect LOS with the GDER.

Another example provides a method 500 for global positioning using aglobal positioning system (GPS) and Doppler augmentation (GDAUG) endreceiver (GDER), as shown in the flow chart in FIG. 5. The methodincludes the operation of generating a GDER position using a time offlight (TOF) of a transponded GPS signal and a Doppler shift in a GDAUGsatellite (GSAT) signal, wherein the transponded GPS signal sent from aGSAT to the GDER comprises a frequency shifted copy of a GPS signal froma GPS satellite to the GSAT, and the GSAT signal comprises a signalgenerated by the GSAT to the GDER, as in block 510.

The operation of generating a GDER position can include: generating asuper-range measurement from the transponded GPS signal, wherein thesuper-range measurement represents a distance from the GPS to the GDERvia the GSAT; measuring a Doppler shift in the GSAT signal; determininga GSAT position by measuring a trend in a plurality of GSAT Dopplershift measurements from a plurality of GSAT signals; calculating a GSATrange from the GSAT position and the super-range measurement of thetransponded GPS signal; and estimating a GDER position using the GSATposition and the GSAT range. The operation of determining the GSATposition can further include: measuring a Doppler shift in thetransponded GPS signal, extracting the Doppler shift due to the GSATrange from the Doppler shift of the transponded GPS signal to generate aDoppler shift of the GPS signal, and estimating the GSAT position usingthe Doppler shift of the GPS signal. The method 500 can further includethe operations of: receiving the plurality of transponded GPS signalsand the GSAT signal; demodulating the plurality of transponded GPSsignals; and detecting the GSAT signal.

Another example provides a method 600 for global positioning using aglobal positioning system (GPS) and doppler augmentation (GDAUG)satellite (GSAT), as shown in the flow chart in FIG. 6. The methodincludes the operation of transmitting a transponded GPS signal, whereinthe transponded GPS signal is a frequency shifted copy of a received GPSsignal from one of a plurality of GPS satellites, as in block 610. Theoperation of transmitting a GSAT signal follows, as in block 620.

The operation of transmitting a transponded GPS signal can include:receiving a GPS signal from a GPS satellite by the GSAT; frequencyshifting the GPS signal to generate a transponded GPS signal; andtransmitting the transponded GPS signal to a GDAUG end receiver (GDER).

In another embodiment, global positioning can be determined using aspace location inertial navigation geopositioning system (SPACELINGS).FIG. 7 illustrates a segment of SPACELINGS, which can be used to provideGPS-type position accuracy to a SPACELINGS end receiver (SER) 720 A-Cusing a high altitude satellite (HAS) 740 to generate (or relay)downlinked pseudo-random noise code (PRN code) signals (or otherGPS-like signals) 742A-B and 742H relayed through a SPACELINGS satellite(SLS) 730A-H. The downlinked PRN signals 742A-B and 742H from the HAS tothe SLS can be represented symbolically by H1 and H2 signals. In otherexamples, H1 and H2 can represent the frequency carriers of the H1 andH2 signals. The transponded PRN signal 732A-D and 732H from the SLS tothe SER can be symbolically represented by a TS1 signal. In otherexamples, TS1 can represent the frequency carrier of the TS1 signal. Adownlink can represent a channel for transmission or a signaltransmitted from a higher altitude device, such as a satellite or ahigher satellite, to a lower altitude device, such as an end receiver, aground station, or a lower satellite. Similarly, an uplink can representa channel for transmission or signal transmitted from a lower altitudedevice, such as an end receiver, a ground station, or a lower satellite,to a higher altitude device, such as a satellite or a higher satellite.

The HAS can have an altitude that exceeds a GPS satellite in a MEO, aGEO, or a high Earth orbit (HEO). The HEO is a geocentric orbit whoseapogee (i.e., the highest or most distant point) lies above that of ageosynchronous orbit. In an example, a MEO satellite can have an orbitalaltitude of approximately 20 km with a near 12 hour orbit. A GEO canhave a near 24 hour orbit, or an orbit near the rotational rate of theEarth, hence geostationary Earth orbit (GEO). The HAS can be furtheraway from the Earth than a GPS satellite, and the HAS can be in a LOS ofmore LEO satellites (such as SLSs and GSATs) than a GPS satellite. Theconstellation of HASs can be smaller than the constellation of GPSsatellites because the HAS can transmit to more LEO satellites (such asSLSs and GSATs). In an embodiment, the constellation of HASs can includeone or two satellites. For example, a GEO satellite can cover or be inthe LOS of three quarters (¾) of the LEO satellites. In contrast, theconstellation of GPS satellites is 24 satellites with some spare orreserve satellites. The higher the orbit of the HAS can reduce thenumber of satellites in the HAS constellation. The HAS constellation canbe a substitute or a redundant global positioning system (GPS) operatingusing different frequencies and/or coding scheme from the GPS.

The SPACELINGS can provide timely space-based positioning, navigation,and timing (PNT) backup or restoration to GPS capability in case GPS iscompletely or partially disabled. The SPACELINGS can provide PNTservices in case of loss of GPS. In addition, the SPACELINGS can provideusers of GPS (e.g., user with a GPS receiver and a SER or an integratedGPS and SPACELINGS end receiver) adequate position and/or navigationinformation when a GPS receiver is jammed, spoofed, or insufficient GPSsatellites are in view of the end receiver. The SPACELINGS can also addprecision to the existing GPS. In an embodiment, the SPACELINGS canremove the dependency on GPS and eliminate a world wide network ofground stations, as is used in GPS. The SPACELINGS can providecapability in cases of a total loss of the GPS, and can augment GPS inenvironments (e.g. urban environments) where obtaining a line of sight(LOS) to at least four GPS satellites can be difficult. The SPACELINGScan provide a significant reduction in complexity and cost of the SLSand SER compared to the GSAT and GDER by having the LEO satellite (e.g.,SLS) transmit on one frequency carrier instead of two frequency carriers(as transmitted by the GSAT), and having the end receiver (e.g., SER)receive one carrier instead of two frequency carriers (as received bythe GDER).

The SPACELINGS can provide PNT restoration and GPS augmentation systemusing very small satellites. The augmentation can provide backup signalsin case a GPS receiver is jammed or spoofed or there are too few GPSsatellites in view. The SLS can be a CUBESAT or other similar type ofsmall or inexpensive type satellite, with functionality similar to theGSAT, but to provide SPACELINGS functionality. SLS can receive signalsfrom the HAS and transpond the signals to a SER, whereas the GSAT canreceive GPS signals from the GPS satellite and transpond the GPS signalsto a GDER as well as generate a GSAT signal and transmit the GSAT signalto the GDER. The SLS payload or hardware on the satellite can be reducedor simplified relative to the GSAT since the SLS can avoid generating anew or independent signal (e.g., GSAT signal).

In an example, SPACELINGS can use a modest size constellation in LEO,where each SPACELINGS satellite (SLS) in LEO has line-of-sight (LOS) toone or more high altitude satellites (HAS), such as GEO satellites. EachHAS can provide a psuedo random noise (PRN) signal on each of two knowncarrier frequencies (or carrier frequencies), such as H1 and H2. In anembodiment, one HAS can cover most of the LEO satellites, and two HAScan provide global coverage to the LEO satellites.

The HAS can generate two PRN code signals (or other GPS-like signals,such as commercial coarse-acquisition (C/A)-type code, a militaryP(Y)-type code, or an M-type code using a varied GPS signal structure)on at least two different carrier frequencies (e.g., H1 and H2). The H1and H2 can operate on a different frequency carrier from a GPS frequencycarrier, such as L1 and L2. The H1 and H2 can operate on a differentfrequency carrier as the common carrier or TS1 signal transmitted fromthe SLS to the SER.

Each SLS acts as a “bent pipe” (similar to a GSAT), transponder relay ofthe downlink PRN signals or HAS signals, as previously discussed withGDAUG. The SLS can detects two analog radio frequency (RF) signals fromthe HAS, can shift each HAS signal, and combine the HAS signals to a newbut common frequency (e.g. TS1). The common frequency of TS1 can be amore favorable, unjammed frequency, which can be frequency hopped in aknown configuration for extra protection against spoofing and jamming.

A receiver on the SLS, which SLS can be in LEO, can “hear” a Dopplershift for each of H1 and H2. The TS1 transponded signal (e.g.,transponded PRN signal) can be “double Doppler shifted” when received bya SER, as discussed below. The “double Doppler shifted” transponded PRNsignal can include the sum of the Doppler shift from the HAS to the SLSand the SLS to the SER (e.g., the user). The two signals can be used bythe end receiver (e.g., SER) to determine the Doppler shift from the HASto the SLS and the remaining Doppler shift from the SLS to the SER, in asimilar manner as described with the GDER.

The SER can despread and/or code the transponded signals to obtain theephemeris of each HAS satellite and the SER can estimate the time ofsignal flight from HAS to SER. The time of flight can provide thetwo-leg “super range” for each HAS transponded signal, where each legrepresents a signal path. Each super range can be the sum of thedistances from HAS to SLS to SER.

The Doppler shift from HAS to SLS can be used by the SER to determinethe ephemeris of each SLS. The SER can then determine the Doppler shiftfrom the SLS to the SER and portion of the super range from SLS to SER.The time history of these range and Doppler shift measurements can beused by the SER to estimate a position of the SER.

The H1 and H2 frequency carriers can differ from the frequency carrierof the TS signal. The H1, H2, and TS1 signals can operate in a frequencyband (a HAS frequency band or a SLS frequency band) between a very highfrequency (VHF) band to a K-under (K_(u)) band. The H1, H2, and TS1signals can operate in a frequency band higher than the frequency bandused for GPS, which can eliminate some of the adverse effects of theionosphere, but the higher frequency may also use more power to transmitthe PRN signals relative to GPS signals.

The two signals on a common carrier have unique Doppler shifts whenreceived by the LEO satellite, which can be used in turn by the endreceiver to deduce the LEO ephemeris. In another example, the doubleDoppler shift can be extracted from two signals, which can be shownmathematically. The HAS can broadcast or transmit the H1 and H2 signalsto the SLS. The SLS can receive

$H\; 1\left( {1 + \frac{v_{1}}{c}} \right)\mspace{14mu}{and}\mspace{14mu} H\; 2\left( {1 + \frac{v_{1}}{c}} \right)$where the v₁ represents the velocity of the HAS relative to the SLS andc represents a speed of light constant (e.g., 299,792,458 meter persecond). The received Doppler shifted H1 and H2 signal can be frequencyshifted by a known frequency, such as plus or minus (±) frequency f, toa common carrier to transmit TS1. The two expressions

$\left( {{H\; 1\left( {1 + \frac{v_{1}}{c}} \right)} + f} \right)\left( {1 + \frac{v_{2}}{c}} \right)\mspace{14mu}{and}\mspace{14mu}\left( {{H\; 2\left( {1 + \frac{v_{1}}{c}} \right)} - f} \right)\left( {1 + \frac{v_{2}}{c}} \right)$received at the SER as TS1 can be measured separately, where v₂represents the velocity of the SLS relative to the SER. The received TS1can include two equations with two unknowns (e.g., V₁ and v₂), whichunknowns can be solved.

In another example, H1 can be frequency shifted by the common frequencycarrier of TS1 by a known frequency f₁, so the H1 component of TS1received at the SER can be represented by

$\left( {{H\; 1\left( {1 + \frac{v_{1}}{c}} \right)} + f_{1}} \right)\left( {1 + \frac{v_{2}}{c}} \right)$t and H1 can be frequency shifted by the common frequency carrier of TS1by a known frequency f₂, so the H2 component of TS1 received at the SERcan be represented by

${\left( {{H\; 2\left( {1 + \frac{v_{1}}{c}} \right)} + f_{2}} \right)\left( {1 + \frac{v_{2}}{c}} \right)},$where the f₁ and f₂ can be positive or negative. The H1 component and H2component of TS1 can be solved for v₁ and v₂. The relative velocity v₁can be used to determine ephemeris of the SLS, and relative velocity v₂can be used to determine ephemeris of the HAS after the ephemeris of theSLS is determined. The H1 component can have a common Doppler component

$\left( {1 + \frac{v_{2}}{c}} \right)$with the H2 component, and H1 component can have a unique Dopplercomponent

$\left( {{H\; 1\left( {1 + \frac{v_{1}}{c}} \right)} + f_{1}} \right)$from a unique Doppler component

$\left( {{H\; 2\left( {1 + \frac{v_{1}}{c}} \right)} + f_{2}} \right)$of the H2 component.

As illustrated in FIG. 8, the high altitude satellite (HAS) 740 caninclude a PRN signal generator 804, a downlink PRN signal transmitter808, at least one SLS transmitting antenna 812, and an optionalamplifier 806. The PRN signal generator can generate the separate H1 andH2 signals on different frequency carriers, which can be transmitted ondownlink PRN signal transmitter via the at least one SLS transmittingantenna. An amplifier may be use to increase or boost the power of thedownlink PRN signal. The high altitude satellite (HAS) may include aprecise clock, such as an atomic clock, used in generating the PRNsignals. The PRN signals may include information similar to a GPSsignal, such as satellite ephemeris or position information or atransmission time, but for the HAS. The H1 and/or H2 signals can betransmitted to the SLS 730 in a simplex transmission.

The separate H1 and H2 signals can be received by the SPACELINGSsatellite (SLS) 730, which can include at least one HAS receivingantenna 810, a HAS signal receiver 820 (like a GPS receiver, but for theHAS) for receiving the HAS signals (e.g., H1 and H2), a frequencyshifter 222 for generating the TS1 signal from the HAS signals (H1and/or H2), at least one SER transmitting antenna 212, and/or atransponded PRN signal transmitter 840 for combining the frequencyshifted H1 and H2 signal and transmitting those signals on a commonfrequency carrier TS1 to the SER 720. The TS1 signals can be transmittedto the SER in a simplex transmission. The SER transmitting antenna canbe a wide angle antenna to cover the Earth from a low orbit. Anamplifier 250 may be use to increase or boost the power of thetransponded PRN signal.

The SPACELINGS end receiver (SER) 720 can include a LEO (e.g., SLS)receiver antenna 310, a transponded PRN signal receiver 822, a signaldespreader 330, and a SPACELINGS module 842. The SER can determine theDoppler shift (and a HAS-to-SLS relative velocity) due to a HAS-to-SLSsignal path and the Doppler shift (and a SLS-to-SER relative velocity)due to a SLS-to-SER signal path, which can be processed by one of themodules of the SER. The SPACELINGS module 842 can generate a globalposition using a TOF super-range measurement and a Doppler shift in aplurality of transponded PRN signals (e.g., H1 and H2 signals). TheSPACELINGS module can include a Doppler shift module 342, a SLSephemeris estimator 844 (which is functions similar to a GSAT ephemerisestimator 844 shown in FIGS. 4A-B, but for a SLS), a range estimator346, and a receiver location estimator 348. In an example, theSPACELINGS module functions similar to the GDAUG module and generates aglobal position, but for transponded PRN signals, whereas the GDAUGmodule used the transponded GPS signals and a GSAT signal.

Another example provides a method 1000 for global positioning using aspace location inertial navigation geopositioning system (SPACELINGS)end receiver (SER), as shown in the flow chart in FIG. 9. The methodincludes the operation of generating a global position using a time offlight (TOF) and a Doppler shift of transponded pseudo-random noise(PRN) signals on a common frequency carrier, wherein the transponded PRNsignals sent from a SPACELINGS satellite (SLS) to the SER comprises afrequency shifted copy of at least two downlink PRN signals from a highaltitude satellite (HAS) to the SLS using at least two differentfrequency carriers from the common frequency carrier, as in block 1010.

In another embodiment, the HAS can generate a single downlink PRN signal(e.g., H1 or H2) which can be transmitted to the SLS. The SLS canfrequency shift the downlink PRN signal to a common frequency carrierTS1 and transmit the signal to the SER or a ground station (e.g., groundsite).

Another example provides a method 1100 for global positioning using aspace location inertial navigation geopositioning system (SPACELINGS)end receiver (SER), as shown in the flow chart in FIG. 10. The methodincludes the operation of generating a global position using a time offlight (TOF) and a Doppler shift of a transponded pseudo-random noise(PRN) signal on a common frequency carrier, wherein the transponded PRNsignal sent from a SPACELINGS satellite (SLS) to the SER comprises afrequency shifted copy of a downlink PRN signal from a high altitudesatellite (HAS) to the SLS using different frequency carrier from thecommon frequency carrier, as in block 1110.

In another embodiment, the HAS can generate a plurality of downlink PRNsignals (e.g., H1 and H2) which can be transmitted to the SLS. The SLScan frequency shift the H1 signal to a first frequency carrier TS1A andfrequency shift the H2 signal to a second frequency carrier TS1B andtransmit both signals via the TS1A and TS1B, respectively, to the SER ora ground station (e.g., ground site).

FIG. 11 illustrates another example of a segment of SPACELINGS. The HAScan include a GPS satellite 140 and the downlink PRN signals can includeGPS signals 146A-B and 146H (e.g., L1 and L2). The SLS 734A-H canreceive the GPS signals (i.e., PRN signals) from the GPS satellite. EachGPS broadcasts a PRN signal on the L1 and the L2 frequency carrier. EachSLS receives the L1 and L2 signals from the GPS satellites in view andtransponds the GPS signals to the common carrier frequency TS1. The SLStransmits the transponded GPS signals to the SER 722A-C and the SERdetermines the global position from the GPS signals (i.e., PRN signals),as previously described. L1 and L2 can undergo different Doppler shifts,proportional to their respective carrier frequencies, when received bythe SLS. The TS1 can be further Doppler shifted as received by SER. TheTS1 signals can be despread and decoded to separately recover theDoppler shifts of L1 and L2, which can be used to estimate the ephemerisof the SLS.

As illustrated in FIG. 12, the GPS satellite 140 can include GPS signalgenerator 904, GPS signal transmitter 908, and at least one GPStransmitting antenna 912. The GPS signal generator can generate theseparate L1 and L2 signals on different frequency carriers, which can betransmitted on GPS signal transmitter via the at least one GPStransmitting antenna.

The separate L1 and L2 signals may be received by the SPACELINGSsatellite (SLS) 734, which can include at least one GPS receivingantenna 210, a GPS signal receiver 820 for receiving the GPS signals(e.g., L1 and L2), a frequency shifter 222 for generating the TS1 signalfrom the GPS signals (L1 and/or L2), at least one SER transmittingantenna 212, and/or a transponded GPS signal transmitter 240 forcombining the frequency shifted L1 and L2 signal and transmitting thosesignals on a common frequency carrier TS1 to the SER 722. The TS1signals can be transmitted to the SER in a simplex transmission. The SERtransmitting antenna can be a wide angle antenna to cover the Earth froma low orbit. An amplifier 250 may be use to increase or boost the powerof the transponded GPS signal. In another example, the SLS can beconfigured to receive GPS signals, HAS signals, and/or other PRNsignals.

The SPACELINGS end receiver (SER) 722 can include a GPS receiver antenna310, a transponded GPS signal receiver 922, a signal despreader 330, anda SPACELINGS module 842. The SER can determine the Doppler shift (and aGPS-to-SLS relative velocity) due to a GPS-to-SLS signal path and theDoppler shift (and a SLS-to-SER relative velocity) due to a SLS-to-SERsignal path, which can be processed by one of the modules of the SER.The SPACELINGS module 842 can generate a global position using a TOFsuper-range measurement and a Doppler shift in a plurality oftransponded GPS signals (e.g., L1 and L2 signals).

Another example provides a method 1200 for global positioning using aspace location inertial navigation geopositioning system (SPACELINGS)end receiver (SER), as shown in the flow chart in FIG. 13. The methodincludes the operation of generating a global position using a time offlight (TOF) and a Doppler shift of a transponded global positioningsystem (GPS) signal on a common frequency carrier, wherein thetransponded GPS signals sent from a SPACELINGS satellite (SLS) to theSER comprises a frequency shifted copy of at least two GPS signals froma GPS satellite to the SLS using at least two different frequencycarriers from the common frequency carrier, as in block 1210.

In another embodiment, the PRN signals can originate at a ground site,which can avoid flying an atomic clock on the HAS. The PRN signals canbe uplinked to one or more HAS (e.g., GEO satellites or other highaltitude platforms) and the PRN signals can be in-turn transponded totwo carrier frequencies. The ground site can also receive the LEOsatellite signals and use them to determine the ephemeris of each LEOsatellite. The uplinked signal can contain the ephemeris information ofeach LEO satellite, the location of the HAS, and the location of theground site. The SER (e.g., end receiver) can use range to the LEOsatellite and Doppler shift from the LEO to estimate the SER position

Using GEO platforms or GEO transponders can work without a world-widenetwork of known ground stations. In addition, one HAS or GEO satellitecan provide signals to LEO satellites covering more than 75% of Earth'ssurface. Two HAS or GEO satellites can provide global coverage withsignificant redundancy.

FIG. 14 illustrates another example of a segment of SPACELINGS withground sites or ground stations (GS) 750. The HAS 744 can function as atransponder (HAS-T) for the GS. The GS can generate at least one uplinkPRN signal G1 752 on a different carrier frequency from H1 or H2 or asame carrier frequency as H1 or H2. The HAS-T can receive the uplink PRNsignal G1 from the GS and transmit the downlink PRN signals H1 and/or H2742A-B and 742H to the SLS. The HAS-T can transpond G1 on to at leastone different carrier frequency (e.g., H1 and/or H2) 742A-B and 742H.The SLS 730 can receive the H1 and H2 signals and can transpond the H1and H2 signals to a different carrier frequency TS1 to the SERs or theGS. The GS can receive the TS1 signal 732E and use the double Dopplershift of the TS1 to estimate the ephemeris of each SLS. G1 can encodethe ephemeris data of the SLS platforms, the ephemeris of each HAS-T,and/or the location of each GS. In an embodiment, the GS can benetworked with other ground stations and exchange the estimated SLSephemerides and estimated HAS ephemerides.

The SER 720A-C can use the PRN signal to compute a super-duper range (arange with 3 separate signal transmission paths and 3 possible Dopplershifts), which can include the signal path from GS 750 to HAS-T 744 toSLS 730A-C to SER 720A-C. Using the encoded information and knowledge ofthe transponder delays the only unknown may be the range from SLS toSER. The component of the Doppler shift from SLS to SER can be extractedusing the known transponder or frequency shifts and the ephemeris of theSLS and the HAS-T. The SER can use the range and Doppler time historyfrom each SLS to estimate a SER position.

As illustrated in FIG. 15, the ground site (GS) 750 can include a PRNsignal generator 854, a PRN signal transmitter 858, and at least one PRNtransmitting antenna 816. The GS can also include a precise clock, likean atomic clock used for the PRN signal generation. The GPS signalgenerator can generate the G1 signal on specified frequency carrier,which can be transmitted on PRN signal transmitter via the at least onePRN transmitting antenna to the HAS-T. An amplifier 856 may be use toincrease or boost the power of the downlink PRN signal.

In another embodiment, the GS 750 can include at least one PRN receivingantenna 860, a transponded PRN signal receiver 850, and a HAS and/or SLSephemeris updater 852. The transponded PRN signal receiver can beconfigured to receive PRN or GPS signals such as TS1 from the SLS. TheHAS and/or SLS ephemeris updater can be used to determine and refine aHAS ephemeris and/or a SLS ephemeris from the super-duper range embeddedin the TS1 signal. In an example, the HAS and/or SLS ephemeris updatercan use the methods and modules similar to those used in the SER todetermine the HAS ephemeris and/or the SLS ephemeris. In an example, theground station position or location can be known which can eliminate anunknown in the super-duper range calculations, so the HAS ephemerisand/or the SLS ephemeris may be determined with a single downlink PRNsignal (e.g., H1 or H2). No clock bias may be used since the PRN signalreceived (e.g., TS1) by the GS originates at GS (e.g., G1) with Dopplershifts, where the same clock used for generation can be used forreception. The Doppler shift for a G1 signal path of the range may bevery small. In another example, the HAS may be a GEO satellite, so theDoppler shift of the G1 signal path may be near zero or a known value(e.g., a correction term), since the GEO satellite is in a relativelyconstant position to the Earth.

In another configuration, the GS 750 can include the at least one PRNreceiving antenna 860, the transponded PRN signal receiver 850, the HASand/or SLS ephemeris updater 852, the signal generator 854, the PRNsignal transmitter 858, and at least one PRN transmitting antenna 816.The HAS and/or SLS ephemeris determined by the HAS and/or SLS ephemerisupdater can be used by the PRN signal generator to correct the HASand/or SLS position information generated for the uplink PRN signal G1.

The high altitude satellite (HAS) 744 or HAS-T can include at least oneGS receiving antenna 814, an uplink GS signal receiver 802, a frequencyshifter 222, downlink PRN signal transmitter 808, at least one SLStransmitting antenna 812, and an optional amplifier 806. The HAS-T canrelay the G1 signal from the GS as the H1 and/or H2 signal(s) to theSLS. The frequency shifter or the downlink PRN signal transmitter cangenerate the H1 and/or H2 signal(s) on different frequency carriers fromthe G1 signal. The amplifier may be use to increase or boost the powerof the downlink PRN signal. The SLS 730 and SER 720 can operate in amanner similar to the SLS and SER previously described but using threesignal paths instead of two signal paths.

The positional accuracy of the SER and the GS can depend on a number ofSLS in view, a time to process, a starting knowledge of position, a SERvelocity, and a SER acceleration. Once an initial SER position isestablished, a very fast convergence can occur to update the SERposition.

The SER position can be initialized with various options, such as userinput, a handover from a last GPS position, signals from two or moreSLS, or extended time measurements with one SLS. In many cases, PRNsignals from a single SLS can provide enough information to locate theposition of the SER. When starting cold (e.g., without any initialposition information), the SER may receive some data from two or moreSLS (at least sequentially) depending on the acceleration of the SER andinformation provided by velocity sensors or INS data associated with theSER. Sequentially as used herein, means two satellites that are visibleto the end receiver at the same time (simultaneously), even if justbriefly, such as one satellite coming above the horizon while anothersatellite is setting behind the horizon. In an embodiment, the SER caninclude an inertial measurement unit (IMU), an inertial navigationsystem (INS), a motion sensor, an accelerometer, a magnetometer, abarometer, a rotation sensor, a gyroscope, wheel counters, odometers, ora combination of these sensors. The sensor may be used to provideinitial position information of the SER and/or velocity or accelerationof the SER which can reduce the time for convergence on the SER positiondetermination.

FIG. 16 illustrates initial performance estimates showingthree-dimensional (3-D) position errors limited by ephemeris errors anda less than 20 m root-means-square (RMS) per axis for North, East, anddown positions for a non-accelerating receiver using PRN signals from asingle SLS without initial position information. The position can bemeasured in meters 104 is determined over time (e.g., seconds 102). Avertical position, such as a down position (e.g., PosDown 166), can takelonger to converge than a horizontal positions, such as a North-Southposition (e.g., PosNorth 162) and East-West position (e.g., PosEast164). Unconstrained motion, such as an accelerating SER, can increasethe time to converge on a position determination of the SER if the SERdoes not include sensor data or other information (e.g., additional SLS)to compensate for the unconstrained motion of the SER. Each constrainton motion such as motion at a known height, such as a ground vehicle,can reduce the time to converge on a position determination of the SERor reduce the number of SLS used to make the SER position determination.

Having a ground site receive and trend data from the HAS-T can improvethe knowledge of the HAS ephemeris (e.g., HAS-T ephemeris) and reducethe time to convergence on the SER position determination.

In an embodiment, the space location inertial navigation geopositioningsystem (SPACELINGS) can restore and/or replace GPS-like capabilitywithout GPS satellites. The SPACELINGS can enables rapid 3-Ddetermination of position for receivers in motion and at rest usingsignals from only one satellite (e.g., SLS), which determination may beachieved more rapid than GDAUG. The SPACELINGS can provide a low costaugmentation to the GPS service. The SPACELINGS can use very small LEOsatellites, including CUBESATs, for a large constellation. In anembodiment, the SPACELINGS can use a small constellation of the moreexpensive HAS relative to the size of the LEO satellites. The SPACELINGScan have significant re-use of existing receiver hardware andtechniques. The performance of SPACELINGS is scalable with size of theLEO satellites and HAS constellation. In an embodiment, most processingcan be offloaded from the space segment of the SPACELINGS to the groundsegment, where components can be cheaper and easier to maintain.

Various techniques, or certain aspects or portions thereof, may take theform of program code (i.e., instructions) embodied in tangible media,such as floppy diskettes, CD-ROMs, hard drives, non-transitory computerreadable storage medium, or any other machine-readable storage mediumwherein, when the program code is loaded into and executed by a machine,such as a computer, the machine becomes an apparatus for practicing thevarious techniques. In the case of program code execution onprogrammable computers, the computing device may include a processor, astorage medium readable by the processor (including volatile andnon-volatile memory and/or storage elements), at least one input device,and at least one output device. The volatile and non-volatile memoryand/or storage elements may be a RAM, EPROM, flash drive, optical drive,magnetic hard drive, or other medium for storing electronic data. Thebase station and mobile station may also include a transceiver module, acounter module, a processing module, and/or a clock module or timermodule. One or more programs that may implement or utilize the varioustechniques described herein may use an application programming interface(API), reusable controls, and the like. Such programs may be implementedin a high level procedural or object oriented programming language tocommunicate with a computer system. However, the program(s) may beimplemented in assembly or machine language, if desired. In any case,the language may be a compiled or interpreted language, and combinedwith hardware implementations.

It should be understood that many of the functional units described inthis specification have been labeled as modules, in order to moreparticularly emphasize their implementation independence. For example, amodule may be implemented as a hardware circuit comprising custom VLSIcircuits or gate arrays, off-the-shelf semiconductors such as logicchips, transistors, or other discrete components. A module may also beimplemented in programmable hardware devices such as field programmablegate arrays, programmable array logic, programmable logic devices or thelike.

Modules may also be implemented in software for execution by varioustypes of processors. An identified module of executable code may, forinstance, comprise one or more physical or logical blocks of computerinstructions, which may, for instance, be organized as an object,procedure, or function. Nevertheless, the executables of an identifiedmodule need not be physically located together, but may comprisedisparate instructions stored in different locations which, when joinedlogically together, comprise the module and achieve the stated purposefor the module.

Indeed, a module of executable code may be a single instruction, or manyinstructions, and may even be distributed over several different codesegments, among different programs, and across several memory devices.Similarly, operational data may be identified and illustrated hereinwithin modules, and may be embodied in any suitable form and organizedwithin any suitable type of data structure. The operational data may becollected as a single data set, or may be distributed over differentlocations including over different storage devices, and may exist, atleast partially, merely as electronic signals on a system or network.The modules may be passive or active, including agents operable toperform desired functions.

Reference throughout this specification to “an example” means that aparticular feature, structure, or characteristic described in connectionwith the example is included in at least one embodiment of the presentinvention. Thus, appearances of the phrases “in an example” in variousplaces throughout this specification are not necessarily all referringto the same embodiment.

As used herein, a plurality of items, structural elements, compositionalelements, and/or materials may be presented in a common list forconvenience. However, these lists should be construed as though eachmember of the list is individually identified as a separate and uniquemember. Thus, no individual member of such list should be construed as ade facto equivalent of any other member of the same list solely based ontheir presentation in a common group without indications to thecontrary. In addition, various embodiments and example of the presentinvention may be referred to herein along with alternatives for thevarious components thereof. It is understood that such embodiments,examples, and alternatives are not to be construed as defactoequivalents of one another, but are to be considered as separate andautonomous representations of the present invention.

Furthermore, the described features, structures, or characteristics maybe combined in any suitable manner in one or more embodiments. In thefollowing description, numerous specific details are provided, such asexamples of layouts, distances, network examples, etc., to provide athorough understanding of embodiments of the invention. One skilled inthe relevant art will recognize, however, that the invention can bepracticed without one or more of the specific details, or with othermethods, components, layouts, etc. In other instances, well-knownstructures, materials, or operations are not shown or described indetail to avoid obscuring aspects of the invention.

While the forgoing examples are illustrative of the principles of thepresent invention in one or more particular applications, it will beapparent to those of ordinary skill in the art that numerousmodifications in form, usage and details of implementation can be madewithout the exercise of inventive faculty, and without departing fromthe principles and concepts of the invention. Accordingly, it is notintended that the invention be limited, except as by the claims setforth below.

What is claimed is:
 1. A global positioning system (GPS) and Doppleraugmentation (GDAUG) end receiver (GDER), comprising: a GDAUG module,wherein the GDAUG module generates a GDER position using a time offlight (TOF) of a transponded GPS signal and a Doppler shift in a GDAUGsatellite (GSAT) signal, and wherein the transponded GPS signal sentfrom a GSAT to the GDER comprises a frequency shifted copy of a GPSsignal from a GPS satellite to the GSAT, and the GSAT signal comprises asignal generated by the GSAT to the GDER, wherein the GDAUG modulefurther comprises: a Doppler shift module that measures a Doppler shiftin the GSAT signal; a GSAT ephemeris estimator that determines a GSATposition by measuring a trend in a plurality of GSAT Doppler shiftmeasurements from a plurality of GSAT signals; a range estimator thatcalculates a GSAT range from the GSAT position and a super-rangemeasurement of the transponded GPS signal, wherein the super-rangemeasurements represents a distance from the GPS to the GDER via theGSAT; and a receiver location estimator that estimates a GDER positionusing the GSAT position and the GSAT range.
 2. The GDER of claim 1,wherein the Doppler shift module measures a Doppler shift in thetransponded GPS signal, and the GSAT ephemeris estimator determines theGSAT position by extracting the Doppler shift due to the GSAT range fromthe Doppler shift of the transponded GPS signal to generate a Dopplershift of the GPS signal and by estimating the GSAT position using theDoppler shift of the GPS signal.
 3. The GDER of claim 1, wherein thereceiver location estimator trends a Doppler shift in a plurality oftransponded GPS signals to generate a GDER position or a GDER velocity.4. The GDER of claim 1, wherein the receiver location estimator furthercomprises an altimeter for determining an altitude of the GDER.
 5. TheGDER of claim 1, wherein the receiver location estimator furthercomprises at least one of a pedometer and an inertial measurement unit(IMU) for determining movement of the GDER.
 6. The GDER of claim 1,wherein the GDAUG module is further configured to decode the transpondedGPS signal to generate a super-range measurement, wherein thesuper-range measurement represents a distance from the GPS to the GDERvia the GSAT.
 7. The GDER of claim 1, wherein the GDAUG module isfurther configured for resetting the clock bias using a plurality oftransponded GPS signals.
 8. The GDER of claim 1, further comprising: aGDAUG signal receiver for receiving the plurality of transponded GPSsignals and the GSAT signal; a signal despreader for demodulating theplurality of transponded GPS signals and detecting the GSAT signal. 9.The GDER of claim 8, wherein the signal despreader is further configuredfor extracting at least one of the time at a GPS satellite, a GPSsatellite location, a GPS satellite identifier, and a GPS satelliteephemeris.
 10. The GDER of claim 1, further comprising: a GPS receiverfor receiving a GPS signal directly from a GPS satellite and fordetermining a global position using a plurality of GPS signals.
 11. Amethod for global positioning using a global positioning system (GPS)and Doppler augmentation (GDAUG) end receiver (GDER), comprising:generating a GDER position using a time of flight (TOF) of a transpondedGPS signal and a Doppler shift in a GDAUG satellite (GSAT) signal,wherein the transponded GPS signal sent from a GSAT to the GDERcomprises a frequency shifted copy of a GPS signal from a GPS satelliteto the GSAT, and the GSAT signal comprises a signal generated by theGSAT to the GDER, wherein generating the GDER position furthercomprises: generating a super-range measurement from the transponded GPSsignal wherein the super-range measurement represents a distance fromthe GPS to the GDER via the GSAT; measuring a Doppler shift in the GSATsignal; determining a GSAT position by measuring a trend in a pluralityof GSAT Doppler shift measurements from a plurality of GSAT signals;calculating a GSAT range from the GSAT position and the super-rangermeasurement of the transponded GPS signal; and estimating a GDERposition using the GSAT position and the GSAT range.
 12. The method ofclaim 11, wherein determining the GSAT position further comprisesmeasuring a Doppler shift in the transponded GPS signal, extracting theDoppler shift due to the GSAT range from the Doppler shift of thetransponded GPS signal to generate a Doppler shift of the GPS signal,and estimating the GSAT position using the Doppler shift of the GPSsignal.
 13. The method of claim 11, wherein estimating the GDER positionfurther comprises trending a Doppler shift in a plurality of transpondedGPS signals to generate a GDER position or a GDER velocity.
 14. Acomputer program product, comprising a non-transitory computer readablestorage medium having a computer readable program code embodied therein,the computer readable program code adapted to be executed to implementthe method of claim 11.